Termites cause substantial damage to residential and commercial buildings in the United States. It has been estimated that the annual cost for controlling termites and repairing their damage in the United States exceeds $1.7 billion. Subterranean termites, the most destructive of all termites, account for 95 percent of this damage. Shripat T. Kamble, internet publication, (http://www.ianr.unl.edu/pubs/insects/g1260.htm).
Subterranean termites most often enter structures from the surrounding soil to feed on wood, or other cellulosic material, of the structure and its contents. Subterranean termites construct an extensive foraging gallery beneath the soil surface. A single colony may contain several million termites with foraging territory extending up to 300 feet (Su, N.Y., R. H. Scheffrahn [1988] Sociobiol. 14(2):353-359). Since subterranean termites are cryptic creatures, their presence is not normally known until after some damage, foraging tubes, or live termites such as swarmers, are found. Some subterranean termites are known to forage beneath an object on the soil surface (Ettershank, G., J. A. Ettershank, W. G. Whitford [1980] Environ. Entomol. 9:645-648).
Control methods for structural infestations of termites varies with the ecology of the different species. Currently, there are two basic approaches for the control of subterranean termites: preventive control and remedial control. In general, preventive measures include the use of wood treated with various repellant chemicals; metal shields between the foundation supports and buildings that either act as barriers, or as a detection method when termites construct visible tubes around the shields; and the creation of chemical barriers by treating the soil under the building foundation, before and after construction, with long-residual termiticides. A layer of basaltic rock particles placed under foundations has been used as a physical barrier to stop the penetration of subterranean termite tunneling. Removal of lumber scraps and sites that accumulate water also discourages the establishment of termite colonies.
Remedial control methods can entail removal of infested wood and replacement with treated wood; drilling and injecting termiticides into small, localized infestations; fumigation of structures with widespread infestations; and use of slow-acting termiticides (Su, N.-Y., M. Tamashiro, and M. I. Haverty (1987) J. Econ Entomol. 80:1-4). Some success has been observed in treating aerial colonies of C. formosanus by the removal of their moisture source. Post-construction soil application of termiticides to eliminate subterranean termite colonies, while commonly attempted, is of limited success (Su, N.-Y., and R. H. Scheffrahn (1990a) J. Econ. Entomol. 83:1918-1924).
In some of the United States, it is mandatory that the soil underlying the foundation of newly constructed buildings be pre-treated with a termiticide to prevent termite infestation. Termiticide is typically sprayed over and into the soil prior to construction. This pre-construction treatment produces a horizontal barrier beneath the building. Because of the lack of communication between pesticide applicator and construction workers, the barrier often loses its continuity during the construction. Moreover, the currently available soil termiticides tend to lose their biological activity after five or more years to the extent that the treated soil is no longer effective against termite invasion. Established termite colonies in the soil may then invade the structure if additional chemical is not applied beneath and around the structure.
When a house or other building is infested by subterranean termites, efforts are made to create a continuous barrier beneath the building in the soil where the subterranean termites are provided access to the building. A common method of creating this barrier is to introduce termiticide around a building foundation by injection into soil underlying concrete foundations, drenching the soil surrounding the building perimeter, or a combination of both. This type of post-construction treatment is labor-intensive and may not adequately produce a continuous barrier (Frishman, A. M., B. L. Bret [1991] Pest Control 59(8):48, 52, 54, 56; Frishman, A. M., A. St. Cyr [1988] Pest Control Technology 16(4):33, 34, 36).
Other remedial treatments include spot treatments such as dusting or injecting termiticides within the walls of the building. Robert Verkerk has described arsenic trioxide dust treatment using termite lures (Verkerk, R. [1990] Building Out Termites, Pluto Press Australia Limited, P.O. Box 199, Leichhardt, NSW 2040). Verkerk describes the use of stakes or blocks of termite susceptible timber to lure termites after the stakes or blocks have been placed near a known termite problem. Once termite activity is observed, arsenic trioxide is injected. Alternatively, a portion of the termites may be dusted with arsenic trioxide.
The effectiveness of the former standard soil termiticides, chlordane and heptachlor, precluded substantial research in alternative termite control methods. Since their withdrawal from the market in 1987, replacement termiticides include chlorpyrifos (Dursban TC) and isofenphos (Pryfon 6), cypermethrin (Demon TC), permethrin (Dragnet FT), fenvalerate (Tribute) and imidacloprid(Premise). Given the loss of chlordane and heptachlor, alternative control measures, such as the use of toxicant and insect growth regulator baits, are being researched (Su, N.-Y., and R. H. Scheffrahn (1990b) Sociology 17:313-328). Concern has been raised about the use of such termiticides, due to their known toxicity. However, because of the devastation termites can cause, and the lack of less toxic, viable alternatives, the EPA has made exemptions for the use of these chemicals as termiticides, despite their known toxicity.
Chemicals used to treat wood for prevention of termite infestation include metallic salts such as mercuric chloride, copper chloride, zinc chloride, ferrous sulphate, wood tar creosote, and coal creosote. Other commonly used wood treatments include arsenic salts. All of the foregoing are known toxic chemicals, and as such are declining in use. As with chemicals used for soil treatments, very few less toxic alternatives exist. Accordingly, there is a substantial need for less toxic alternatives for preventing and treating termite infestation, as well as infestations by other wood-boring insects including, but not limited to, carpenter ants, carpenter bees, and powderpost beetles.